1. Field of the Invention
The invention relates to a method of preparing chromans and more particularly relates to the method of preparing chromans by the reaction of diacetone alcohol with a phenolic compound.
2. Brief Description of the Prior Art
Chroman-I, i.e.; p-[2,2,4-trimethyl-4-(4-hydroxyphenyl)chroman] is a well known compound useful to terminate polycarbonate resins; see for example U.S. Pat. No. 3,697,481. It was first obtained by Dianin in 1914, from the reaction of phenol, mesityl oxide and hydrogen chloride, by a slow process (4 weeks). A flavan structure was incorrectly assigned; A. P. Dianin, J. Russian Physical Chemical Society, 46, 1310 (1914). The correct structure was determined by Baker, et al., via degradation; they also reduced reaction time to 4 days, and obtained a 36% yield (W. Baker, et al., J. Chem. Soc., 1965, 2010). The structure was confirmed by rational synthesis (W. Baker, et al., ibid, 1956, 2018). More recently, the compound was obtained by isolation from bisphenol-A streams by its adduction with ethanol; see Netherlands Patent Application, No. 6,515,583.
The method of the present invention employs relatively inexpensive reactants and results in commercially important yields with favorable economic advantages.